BIODIVERSITY IMPACTS and SUSTAINABILITY IMPLICATIONS of CLEARFELL LOGGING in the WELD VALLEY, TASMANIA Graham Green1, Alan Gray2, Dr Peter McQuillan3 1. Timber Workers for Forests 2. Consultant Botanist and Forest Ecologist 3. Entomologist, University of Tasmania March 2004 Copyright A Timber Workers for Forests publication Phone: (03) 6239 1630 or 0422 936027 Mail: PO Box 101, Kingston TAS 7051 Fax: (03) 6229 7629 Email: [email protected] Web: www.twff.com.au Funded by the Mullum Trust 1 Executive Summary This study was undertaken in the Weld River Valley, an area of largely pristine forest located in Tasmania’s southern forests just north of the Tahune Airwalk tourism venture. The study was conducted in order to compare and contrast the botanical diversity, soil ecology, invertebrate biodiversity and timber values of old growth forest in the valley with a nearby forest coupe that was clearfelled in the 1980s. The findings of the study are used to give an independent critique of the scientific basis used to justify the ‘clearfell, burn and sow’ silvicultural system which dominates forestry in Tasmania today. The study demonstrated that logging old growth forest in the Weld Valley significantly alters the diversity and abundance of plants and invertebrates. Poor soil structure and lack of soil humus following the clearfell burn and sow treatment appears to adversely affect forest health and its ability to produce good timber. In sites regenerated following clearfelling there was significant root and crown competition resulting in slow and poor tree growth. A key measure of sustainability is that no species are lost from an ecosystem. The claim that ‘no species are known to have been driven to extinction by forestry practices in Tasmania’ heavily relies on the lack of knowledge about the species which live in Tasmania’s native forests, and the fact that we know little about the long-term effects of forest fragmentation and conversion to plantations of exotic species. The sampling of nocturnal insects at old-growth and regrowth study sites in the Weld Valley highlighted the stark differences in the diversity of animals present. Using native moths as an indicator of biodiversity it was revealed that: • old growth forest supported many more species (81 versus 39) • old growth forest supported a higher proportion of species endemic to Tasmania (22% versus 6%) • old growth forest had a high proportion of species which rely on fungi, leaf litter and decaying wood • regrowth forest had fewer species, but some were extremely abundant, indicative of pest status • regrowth forest had some species which have adapted to live on weeds. Native forests managed on short rotation cycles will never reproduce the diverse micro-habitats which characterise old forests. This study brings in to question whether the forests allocated for timber production under the Regional Forest Agreement (RFA) have been managed in an ecologically sustainable way, that is, in a way that maintains species diversity, water resources, and soil structure and quality. Forest health, and the ability of the forest to continue to produce healthy timber in perpetuity, is intimately linked to the maintenance of biodiversity and soil health. If biodiversity is compromised, then timber production areas will become more degraded with each clearfell 2 rotation. This has serious implications, not just for forest ecology and biodiversity, but also for a suite of social and economic values such as: future timber quality, aesthetics, ecotourism opportunity, beekeeping and pollination services, and water supply. The scientific basis for clearfelling derived from research undertaken in the 1950s must now come under question and should now be critically reviewed in light of the biodiversity implications highlighted in this study. The study has provided a strong case for a moratorium on logging in the Weld Valley which is an area that has been identified for its high conservation values and significant ecotourism potential. The case for a moratorium on logging is strengthened in light of the current sawlog oversupply and a glut in specialty timbers. Acknowledgements We are grateful to the Mullum Trust for funding this study. Many people assisted with fieldwork, collection of data and photography, especially Wally Herrmann, members of TWFF, Adam Burling, Neil Sorensen and Janet Dyment. Matt Dell is thanked for preparation of maps of the Weld Valley. Benedict Bartl, Liam Mulchay & Phil Pullinger are thanked for supplying background material about the Weld Valley in their document ‘Expanding the Airwalk Experience - a proposal for the Huon Valley Council’. 3 Table of Contents EXECUTIVE SUMMARY................................................................................................................ 2 ACKNOWLEDGEMENTS............................................................................................................... 3 1.0 INTRODUCTION.................................................................................................................. 5 2.0 BACKGROUND TO THE WELD VALLEY.................................................................... 6 3.0 STUDY SITES AND METHODOLOGY........................................................................... 7 3.1 METHODS .............................................................................................................................. 9 4.0 BOTANY AND SOIL ECOLOGY.................................................................................... 10 4.1 STUDY SITE ONE – OLD GROWTH FOREST WR17B............................................................. 10 4.1.1 Floristic structure ...................................................................................................... 12 4.2 STUDY SITE TWO – REGROWTH FOREST WR015H............................................................. 14 5.0 INVERTEBRATE ECOLOGY.......................................................................................... 15 6.0 CONCLUSION.....................................................................................................................16 6.1 SAWLOG OVERSUPPLY ........................................................................................................16 6.2 GLUT OF SPECIALTY TIMBERS ............................................................................................ 16 6.3 QUESTION MARKS OVER THE SCIENTIFIC BASIS OF CLEARFELLING ................................... 17 APPENDIX A – MOTH SPECIES IDENTIFIED IN THE WELD VALLEY....................... 18 4 1.0 Introduction This study was undertaken in the Weld River Valley, an area of largely pristine forest located on the eastern fringe of the Tasmanian Wilderness World Heritage Area, approximately 60 km west- south-west of Hobart, just to the north of the Tahune Airwalk tourism venture. The primary intention of this study was to categorise the biodiversity of an old growth forest coupe (called WR17B by Forestry Tasmania) prior to logging, which is due for commencement in March 2004. The study will provide a benchmark from which to gauge the impact of logging on the long-term biodiversity of the site. The other primary intention of this study was to compare and contrast the botanical diversity, soil ecology, invertebrate biodiversity and timber values of the old growth forest in WR17B with a nearby forest coupe regenerated following clearfelling in the 1980s. The findings of the study are used to give an independent critique of the scientific basis for the ‘clearfell, burn and sow’ silvicultural system which is the dominant harvesting and regeneration system in Tasmania today. ‘Science’ is frequently used as the basis for justifying logging practices in Tasmania. Opponents of industrialised forestry, which is characterised by clearfelling, are frequently criticised for being irrational, emotional or ‘ignoring the facts’ or ‘ignoring the science’. The scientific justification for the ‘clearfell, burn and sow’ silvicultural system arose from a University thesis written by John Gilbert in 19581. At the time Gilbert acknowledged that his methodology was efficient for regenerating Eucalypts but conceded that there were other ecological shortcomings. Nearly 50 years on, the silvicultural system proposed in Gilbert’s thesis is still being used unquestioningly despite significant community concern over the impacts of the ‘clearfell, burn and sow’ system. Tasmania’s RFA (Regional Forest Agreement) has also been much touted as being ‘scientifically based’. While it is true that teams of scientists were engaged in a flurry of activity to identify a comprehensive and adequate reserve system for Tasmania’s major vegetation communities, six years on there remains conjecture as to whether the reservation targets have actually been met. The findings of this study are used to assess whether logging by clearfelling and associated logging treatments can be sustained in the forests of the Weld Valley and whether the scientific basis of modern day forestry can still be justified. 1 Gilbert, J. (1958). Eucalypt-rainforest relationships and the regeneration of eucalypts. PhD thesis, Botany Department, University of Tasmania. 5 2.0 Background to the Weld Valley The Weld River Valley is located adjacent to the Tasmanian Wilderness World Heritage Area, about 60 km west-south-west of Hobart. The Weld River has a length of 50 km 2 and its catchment ‘contains one of the largest karst areas in Tasmania, including Australia’s deepest cave, a natural river arch